Motorola MVME172 User Manual download pdf (Page 180)

2-102 Computer Group Literature Center Web Site

VMEchip2

The location monitor status register provides the status of the location

monitors. A location monitor bit is cleared when the VMEchip2 detects a

VMEbus cycle to the corresponding location monitor address. When the

LM0 or LM1 bits are cleared, an interrupt is set to the local bus interrupter.

If the LM0 or LM1 interrupt is enabled in the local bus interrupter, then a

local bus interrupt is generated. The location monitor bits are set by writing

a one to the corresponding bit in the location monitor register. LM0 and

LM1 can also be set by writing a one to the corresponding clear bits in the

local interrupt clear register.

The interrupt control register provides four bits that allow the VMEbus to

interrupt the local bus. An interrupt is sent to the local bus interrupter when

one of the bits is set. If the interrupt is enabled in the local bus interrupter,

then a local bus interrupt is generated. The interrupt bits are cleared by

writing a one to the corresponding bit in the interrupt clear register.

The board control register allows a VMEbus master to reset the local bus,

prevent the VMEchip2 from driving the SYSFAIL signal line, and detect

if the VMEchip2 wants to drive the SYSFAIL signal line.

The six general purpose registers can be read and written from both the

local bus and the VMEbus. These registers are provided to allow local bus

masters to communicate with VMEbus masters. The function of these

registers is not defined by this specification. The GCSR supports

read-modify-write cycles such as TAS.

Caution

The GCSR allows a VMEbus master to reset the local bus.

This feature is very dangerous and should be used with

caution. The local reset feature is a partial system reset, not a

complete system reset such as powerup reset or SYSRESET.

When the local bus reset signal is asserted, a local bus cycle

may be aborted. The VMEchip2 is connected to both the local

bus and the VMEbus and if the aborted cycle is bound for the

VMEbus, erratic operation may result. Communications

between the local processor and a VMEbus master should use

interrupts or mailbox locations; reset should not be used in

normal communications. Reset should be used only when the

local processor is halted or the local bus is hung and reset is

the last resort.

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Motorola MVME172 User Manual Page 180